1. Field of the Invention
The present invention relates to an optical fiber and a waveguide used for optical amplification at 1.65 .mu.m Wavelength band and other wavelength bands, and an optical active device using the same.
2. Related Background Art
Many efforts have been made to manufacture a fiber amplifier by using an optical fiber to which a rare-earth element such as Nd is added, in order to apply it to the field of optical communication at 1.3 .mu.m band, 1.55 .mu.m band, and the like. Furthermore, a fiber amplifier at, e.g., 1.65 .mu.m wavelength band is now required to be used for a failure detection system for the maintenance and the like of an optical communication system of 1.55 .mu.m band. Such a fiber amplifier is required since 1.65 .mu.m band is longer than 1.55 .mu.m band and is an operation band of a semiconductor laser.